The detection of microbial contaminants, often referred to as “bioburden,” is a practice commonly used to ensure the safety, quality, and purity of many fluids encountered in everyday life. Bioburden detection includes monitoring microbial contamination in drinking and industrial water supplies, foods, beverages, research materials (such as tissue culture media), and pharmaceutical preparations. Monitoring is as important to biodefense, where contamination could result from intentional acts of aggression, as it is for industry and consumers, where contamination is typically unintentional.
Traditional methods of determining the presence of contaminating microorganisms in liquids rely on culturing a sample suspected of contamination in a liquid or agar-based medium to increase the number of microorganisms to a detectable level. The sample may be inoculated directly into the culture medium or may first be concentrated by filtration to capture microorganisms for culture. In either case, it may be several days before any microorganism present in the sample can be detected, which can, for example, involve visualizing microbial growth or detecting a byproduct of bacterial metabolism that results in a change in temperature, pH, turbidity, color, bioluminescence, and/or impedance of the culture. Subsequent testing to identify a contaminating microorganism by traditional microbiological methods can add days or weeks to the procedure. Relying on growth in culture requires that an initial educated guess is made of the appropriate culture conditions for an unknown contaminant. Where two or more microorganisms are present in a sample, one may be more suited to the conditions selected (i.e. more “culturable”), resulting in overgrowth of one microorganism, which may obscure the presence of additional organisms in the sample. Consequently in a mixed sample, the presence of some organisms may be overlooked. Pathogenic microorganisms include many that can be “infectious but not culturable” and may therefore go undetected by methods that require a culturing step. For example, certain disinfection-injured bacteria found in the ultra-pure or chlorinated water systems are known to be very difficult to culture.
Thus, there remains a clear need for highly sensitive, rapid and inexpensive devices and methods for detecting bioburden contamination in water treatment and food testing stations, health-care facilities, research laboratories, public buildings and other situations where microbial contamination cannot be tolerated.